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Myeloproliferative neoplasm without marked myelofibrosis, compatible with essential thrombocythaemia.
Bone Marrow, Iliac Crest
Haematoxylin & Eosin (H&E)
42 years
42-year old male patient. Clinical suspicion for myeloproliferative neoplasm (essential thrombocythaemia). Genetics: mutation for JAK 2 is negative.
Representative core biopsy with age-correlated normocellular bone marrow (50%). Megacaryocytes are increased in number (up to 10 megacaryocytes/HP field) and show enlarged, hyperlobulated, (stag-horn-like) nuclei. Erythropoiesis is inconspicuous. Myelopoiesis shows normal maturation without increase in blasts.
Fibre stain shows myelofibrosis grade 0 with some foci of minimal increase in reticulin fibres (myelofibrosis grade 1). There is evidence of storage iron, focally pronounced.
WHO criteria for essential thrombocythaemia (meeting all four criteria is required for diagnosis): 1. Sustained platelet count >450 x10^9/L 2. Bone marrow biopsy showing increased number of enlarged, mature megacaryocytes. No increase or left-shift of granulopoiesis or erythropoiesis. 3. Not meeting criteria for other MPN or MDS. 4. Demonstration of JAK2 or other clonal marker (CALR, MPL). If negative for JAK2 no evidence for reactive thrombocytosis.
Andrea Bodmer, University of Basel
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